Photochromic diarylethene-containing coordination compounds and the production thereof

ABSTRACT

Diarylethene-containing ligands and their coordination compounds are described. The ligands display photochromism with UV excitation, while the coordination compounds display photochromism with both excitation in the UV region and excitation into lower energy absorption bands characteristic of the coordination compounds, through which the excitation wavelengths for the photocyclization can be extended from λ≦340 nm to wavelengths beyond 470 nm. Switching of the luminescence properties of the compounds has also been achieved through photochromic reactions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/883,677 filed Jul. 6, 2004 now U.S. Pat. No. 7,355,755,which claims the benefit of U.S. provisional patent application No.60/484,668 filed Jul. 7, 2003, the entirety of both disclosures beingincorporated herein by reference.

FIELD OF THE INVENTION

This invention is related to the design and the photochromic behavior ofnovel photochromic ligands and their coordination compounds. The designof these photochromic ligands and their coordination compounds is basedon the cis-diarylethene structure, which forms part of a mono- orpoly-cyclic ring structure that contains one or more donor atom(s) ordonor heteroatom(s) for coordination to an acceptor atom to formphotochromic coordination compounds.

BACKGROUND OF THE INVENTION

Photochromism is defined as “a reversible transformation of a singlechemical species being induced in one or both directions by absorptionof electromagnetic radiation, with two states having differentdistinguishable absorption spectra.” Thus, photochromic compounds arecompounds that possess at least two isomeric forms which have differentphysical properties, such as absorption properties, refractivity, andthe like, and can be transformed from one form to another by lightexcitations at prescribed wavelengths.

Photochromism has been intensively studied due to its potential use foroptical recording and other optical functioning devices. To bepractically used as optical recording materials, both isomeric formsmust be thermally stable and possess excellent durability for reversiblephotochromic reactivity. Diarylethene is one class of photochromiccompounds which possesses these properties, and therefore is a suitableclass of compounds for the construction of optical functioning devices.The cis-configuration of both aryl groups in the diarylethenes studiedis generally fixed by an upper cycloalkene structure, such asfluorinated alicyclic group, aromatic group, anhydride and maleimidegroup. Apart from the difference in absorption characteristics and thelike between the two forms and their thermal stabilities, theavailability of desirable excitation wavelengths that can be tuned andselected for the photochromic reactions also represents an importantaspect in the design of materials for optical functioning devices. Ithas been shown that with the more π-conjugated upper cycloalkenestructures, such as maleimide derivatives, in the diarylethenecompounds, the photocyclization proceeded with lower energy excitationin the visible region.

Further information can be found in U.S. Pat. Nos. 5,175,079, 5,183,726,5,443,940, 5,622,812, and 6,359,150; Japanese patents JP 2-250877, JP3-014538, JP 3-261762, JP 3-261781, JP 3-271286, JP 4-282378, JP5-059025, JP 5-222035, JP 5-222036, JP 5-222037, JP 6-199846, JP10-045732, JP 2000-072768, JP 2000-344693, JP 2001-048875, JP2002-226477, JP 2002-265468 and JP 2002-293784; and in Irie et al.,“Thermally Irreversible Photochromic Systems. ReversiblePhotocyclization of Diarylethene Derivatives”, Journal of OrganicChemistry, 1988, 53, 803-808, Irie et al., “Thermally IrreversiblePhotochromic Systems. A Theoretical Study”, Journal of OrganicChemistry, 1988, 53, 6136-6138, and Irie, “Diarylethenes for Memoriesand Switches”, Chemical Review, 2000, 100, 1685-1716. The photochromiccompounds of this invention can be used in the same way as described inthese references.

SUMMARY OF THE INVENTION

The present invention relates to the use of coordination compounds toperturb the properties of the diarylethenes in photochromic compounds.Described below is a report of the design, synthesis and studies ofcis-diarylethene-containing ligands, with the upper cycloalkene beingpart of a mono- or poly-cyclic ring structure that contains one or moredonor atom(s) or donor heteroatom(s), such as phenanthrolines,pyridines, imidazoles, pyrazoles, thiazoles, pyrroles, diazines,triazines, polypyridines, porphyrins and phthalocyanines and the like,for coordination compound formation.

The object of the present invention is to provide a new class ofdiarylethene-containing coordination compounds capable of displayingperturbed and sensitized photochromic properties. The inventedphotochromic compound is a coordination compound that contains adiarylethene with one or more donor atoms coordinated to an acceptoratom of the coordination compound. Any diarylethene in which the ethenegroup in a heterocyclic moiety, monocyclic or polycyclic, with any donoratom(s) capable of forming a coordination compound can be used in thepresent invention. There is no restriction on the nature of the arylgroups and they can be heteroaryl groups such as, for instance, thienylgroups. Likewise, any acceptor atoms which can be coordinated with theethene-containing heterocyclic ligand moiety can be employed.

In a preferred form, the photochromic coordination compound is expressedby the following general formula (I):

where unit B represents a mono- or poly-cyclic ring structure, such asphenanthroline, pyridine, imidazole, pyrazole, thiazole, pyrrole,diazine, triazine, polypyridine, porphyrin and phthalocyanine and thelike, that contains one or more donor atom(s) X, such as carbon, ordonor heteroatom(s) X, such as nitrogen, oxygen, sulfur, phosphorus,selenium, i.e., n is integer from 0 to 3, [M] represents thecoordination unit containing an acceptor atom M, such as rhenium(I),zinc(II), ruthenium(II), osmium(II), rhodium(III), iridium(III),gold(III), gold(I), silver(I), copper(I), copper(II), platinum(II),palladium(II), iron(II), cobalt(III), chromium(III), cadmium(II),boron(III) and the like, R₁ and R₆ individually represent alkyl groupsand alkoxy groups, and R₂ to R₅ individually represent atoms or groupsselected from the group of hydrogen atom, halogen atom, hydroxyl group,alkyl group, alkoxy group, alkynyl group, cyano group, nitro group,alkylcarbonyl group, alkoxycarbonyl group, perfluoroalkyl group, arylgroup, cycloalkyl group, arylcarbonyl group, aryloxycarbonyl group,mono- or dialkylaminocarbonyl group, alkylcarbonyloxy group,arylcarbonyloxy group, aryloxy group, alkoxycarbonyl group,aryloxycarbonyloxy group, and the like. In general, any alkyl or alkoxygroup contains 1 to about 20 carbon atoms, any cycloalkyl group contains3 to 8 carbon atoms, and any aryl group contains 6 to about 20 carbonatoms.

A non-limiting list of examples of diarylethene compounds containing aheterocyclic ethene-containing ligand moiety includes5,6-dithienyl-1,10-phenanthroline,2,3,7,8,12,13,17,18-octathienyl-5,10,15,20-tetraphenyl porphyrin,6,7-dithienyl-dipyrido[3,2-a:2′,3′-c]phenazine and the like.

A non-limiting list of coordination units includeschlorotricarbonylrhenium(I), dithiolatozinc(II), dihaloplatinium(II),bipyridylplatinum(II), bis[bipyridyl]ruthenium(II),diphosphinocopper(I), bipyridylcopper(I) and the like.

One of the advantages of the formation of coordination compounds fromtheir pure organic counterparts (free ligands) in this invention is theextension of the excitation wavelength for the photocyclization of thediarylethene moiety from λ≦340 nm to lower energy, so that thephotochromic forward reaction can proceed with visible light excitationby utilization of the low-energy absorptions characteristic ofcoordination compounds. In addition, the photochromic reactions can beutilized to switch the photoluminescence properties characteristic ofthe coordination compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a representative synthetic route for adiarylethene-containing ligand and its coordination compounds using5,6-dithienyl-1,10-phenanthroline and its chlorotricarbonylrhenium(I)and dithiolatozinc(II) compounds as illustrative examples.

FIG. 2 shows the overlaid electronic absorption spectra of the open form(-) and the close form (- -) of a diarylethene-containing nitrogen donorligand (L1).

FIG. 3 shows the overlaid electronic absorption spectra of the open form(-) and the close form (- -) of a diarylethene-containing coordinationcompound (1).

FIG. 4 shows the photochromic reactions of (a) a diarylethene-containingligand and (b) its coordination compound using5,6-dithienyl-1,10-phenanthroline and its chlorotricarbonylrhenium(I)compound as illustration.

FIG. 5 shows the overlaid corrected emission spectra of the open form(-) and the close form (- -) of (1) in benzene solution at 298 K.

FIG. 6 shows the overlaid corrected emission spectra of the open form(-) and the close form (- -) of (1) in EtOH-MeOH (4:1 v/v) glass at 77K.

FIG. 7 shows the absorption spectral changes of complex (4) in benzeneupon excitation at λ=300 nm.

FIG. 8 shows a representative synthetic route fordiarylethene-containing ligands and their coordination compounds using1-(aryl)-bis-(2,5-dimethyl-3-thienyl)-2-(2-pyridyl)imidazoles and theirchlorotricarbonylrhenium(I) compounds as illustrative examples.

FIG. 9 shows (a) the absorption and (b) emission spectral changes ofcomplex (6) in degassed chloroform solution (7.16×10⁻⁵ M) upon MLCTexcitation at λ=410 nm.

FIG. 10 shows a representative synthetic route for adiarylethene-containing ligand and its coordination compounds using1,3-dimethyl-4,5-bis-(2,5-dimethyl-3-thienyl)-imidazoliumhexafluorophosphate and its diiodopalladium(II) compounds asillustrative examples.

FIG. 11 shows the absorption spectral changes of complex (7) indichloromethane solution (1.21×10⁻⁴ M) upon excitation at λ=310 nm.

FIG. 12 shows a representative synthetic route fordiarylethene-containing ligand and its coordination compounds using5-ethynyl-2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiophene and itsbis(triethylphosphine)platinum(II) compounds as illustrative examples.

FIG. 13 shows the absorption spectral changes of complex (8) indichloromethane solution (3.10×10⁻⁴ M) upon excitation at λ=400 nm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

The ligand (L1) is synthesized by the Suzuki cross-coupling reactions of2.5 equivalents of 2,5-dimethyl-3-thienylboronic acid and5,6-dibromo-1,10-phenanthroline in the presence of the palladiumcatalyst, Pd(PPh₃)₄, and sodium carbonate in a heterogeneous mixture ofwater and THF according to the synthetic route depicted in FIG. 1.Excitation of (L1) with 313 nm light resulted in the formation of theclose form, corresponding to the photocyclization product. The overlaidelectronic absorption spectra of the open and close forms of (L1) inbenzene solution are shown in FIG. 2.

Upon coordination to a chlorotricarbonylrhenium(I) complex, the openform of the corresponding complex (1) undergoes photocyclization withthe excitation of both the intraligand absorptions at λ≦340 nm and themetal-to-ligand charge transfer (MLCT) absorption characteristic of thiscoordination compound up to λ≦480 nm. The electronic absorption data of(L1) and complex (1) are summarized in Table 1. The close forms of thesecompounds are found to undergo thermal backward reactions. Thehalf-lives of the close forms have been determined and summarized inTable 2. The quantum yields for both photocyclization andphoto-cycloreversion of (L1) and its rhenium complex (1) are summarizedin Table 3.

TABLE 1 Absorption (in benzene) Compound Configuration λ_(abs)/nm (ε/dm³mol⁻¹ cm⁻¹) (L1) Open form 304 (8670) (L1) Close form 366 (24340), 510(4050), 540 (3860) (1) Open form 338 (4930), 396(4690) (1) Close form390 (36670), 546 (5390), 580 (5050)

TABLE 2 Compound Half-lives (t_(1/2)) at 20° C. Half-lives (t_(1/2)) at60° C. (L1)  143 hours  222 mins (1) 77.7 hours 79.3 mins

TABLE 3 Photochemical Quantum Yield/φ Photocyclization^(a)Photo-cycloreversion Compound φ313 φ440 φ365 φ510 (L1) 0.486 0 0.1230.029 (1) 0.552 0.648 0.028 0.009 ^(a)Values reported are corrected tothe ratio of the photochromic active conformation, i.e. with respect tothe anti-parallel configuration

The photoluminescence properties of both the open and close forms weremeasured. FIGS. 5 and 6 display the overlaid emission spectra of theopen form and the close form of complex (1) in benzene at 298 K and inEtOH-MeOH glass (4:1 v/v) at 77 K. The emission of complex (1) was foundto change from metal-to-ligand charge transfer (MLCT) phosphorescence toligand-centered (LC) phosphorescence upon photocyclization of the openform to the close form. These demonstrate the change of emissionproperties upon photochromic reactions. Table 4 summarized the emissiondata of ligand (L1) and complex (1).

TABLE 4 Emission λ_(em) ^(a)/nm (τ_(o)/μs) Compound Medium (T/K) Openform Close form (L1) Benzene (298) 383 (<0.1) 644 (<0.1) Glass^(b) (77)—^(c) 577 (5.2) (1) Benzene (298) 595 (0.26) 626 (<0.1) Glass^(b) (77)535 (7.2) 620 (6.4) ^(a)Excitation wavelength at ca. 355 nm. Emissionmaxima are corrected values. ^(b)EtOH—MeOH (4:1, v/v) ^(c)Non-emissive

Example 2

Upon coordination of (L1) to a dithiolatozinc(II) complex, the openforms of the corresponding complexes (2), (3) and (4) undergophotocyclization with excitation at λ≦340 nm. FIG. 7 shows theabsorption spectral changes of complex (4) upon excitation at λ=300 nm.The electronic absorption maxima of both the open and the close forms ofcomplexes (2), (3) and (4) are summarized in Table 5.

TABLE 5 Absorption maximum (in benzene) Complex Configuration λ_(abs)/nm(2) Open form 302, 326, 378 (2) Close form 366, 382, 536, 576 (3) Openform 302, 326, 382 (3) Close form 366, 382, 538 (4) Open form 302, 336,396 (4) Close form 366, 384, 542, 584

Those skilled in the art will recognize that various changes andmodifications can be made in the invention without departing from thespirit and scope thereof. The various embodiments described were for thepurpose of further illustrating the invention and were not intended tolimit it.

Example 3

The ligands,1-(4-methoxyphenyl)-bis-(2,5-dimethyl-3-thienyl)-2-(2-pyridyl)imidazole(L2) and1-(4-methylphenyl)-bis-(2,5-dimethyl-3-thienyl)-2-(2-pyridyl)imidazole(L3), are synthesized by Suzuki cross-coupling reactions of 2.5equivalents of 2,5-dimethyl-3-thienylboronic acid and1-aryl-4,5-dibromo-2-(2-pyridyl)imidazole in the presence of thepalladium catalyst, Pd(PPh₃)₄, and sodium carbonate in a heterogeneousmixture of water and THF according to the procedure similar to that of(L1) as depicted in FIG. 8. Excitation of (L2) and (L3) with 313 nmlight resulted in the formation of the close form, corresponding to thephotocyclization product.

Similar to ligand (L1), upon coordination of (L2) and (L3) tochlorotricarbonylrhenium(I) complex, the open form of the correspondingcomplexes (5) and (6) undergo photocyclization with the excitation ofboth the intraligand absorptions at λ≦370 nm and the metal-to-ligandcharge transfer (MLCT) absorption characteristic of this coordinationcompound up to λ≦470 nm. The electronic absorption data of ligands(L2)-(L3) and complexes (5)-(6) are summarized in Table 6. Apart fromthe change in the absorption properties, the emissions of all thecomplexes were also found to drop significantly upon conversion to theclose form. These further illustrate the change of emission propertiesupon photochromic reactions. The representative emission and electronicabsorption spectral changes of the open form in chloroform solution uponphoto-irradiation are shown in FIG. 9.

TABLE 6 Absorption maximum (in chloroform) Compound Configurationλ_(abs)/nm (L2) Open form 320 (L2) Close form 330, 425, 586 (L3) Openform 319 (L3) Close form 334, 410, 576 (5) Open form 352, 425sh (5)Close form 284, 374, 475, 712 (6) Open form 353, 425sh (6) Close form286, 376, 480, 713

Example 4

The ligand, 1,3-dimethyl-4,5-bis-(2,5-dimethyl-3-thienyl)-imidazoliumhexafluorophosphate (L4), is synthesized by the methylation of4,5-bis-(2,5-dimethyl-3-thienyl)-1H-imidazole, which is also preparedusing Suzuki cross-coupling reactions of 2.5 equivalents of2,5-dimethyl-3-thienylboronic acid and 4,5-dibromo-1H-imidazole in thepresence of the palladium catalyst, Pd(PPh₃)₄, and sodium carbonate in aheterogeneous mixture of water and THF according to the proceduresimilar to that of (L1), as depicted in FIG. 10. Excitation of theligand with λ≦290 nm light resulted in the formation of the close form,corresponding to the photocyclization product.

Upon coordination to palladium(II) iodide to form thebis[1,3-dimethyl-4,5-bis(2,5-dimethyl-3-thienyl)-imidazol-2-ylidene]diiodopalladium(II)complex, the open form of the corresponding complex (7) undergoesphotocyclization with the excitation of both the intraligand absorptionsat λ≦290 nm and the absorption characteristic of this coordinationcompound up to λ≦320 nm. The electronic absorption data of ligand (L4)and complex (7) are summarized in Table 7. The representative electronicabsorption spectral changes of complex (7) in dichloromethane solutionupon photo-irradiation are shown in FIG. 11.

TABLE 7 Absorption maximum Compound Configuration (in dichloromethane)λ_(abs)/nm (L4) Open form 235 (L4) Close form 350, 580 (7) Open form240, 305 (7) Close form 345, 540

Example 5

5-Trimethylsilylethynyl-2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiopheneis synthesized by the Sonogashira coupling reaction oftrimethylsilylacetylene and the bromo-derivative of2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiophene, which is alsoprepared from the Suzuki cross-coupling reaction of 2.5 equivalents of2-methyl-3-benzo[3,2-b]thienylboronic acid and 2,3-dibromothiophene inthe presence of the palladium catalyst, Pd(PPh₃)₄, and sodium carbonatein a heterogeneous mixture of water and THF according to the proceduresimilar to that of (L1). Subsequent deprotection of the trimethylsilylgroup using potassium carbonate in dichloromethane solution gives thetarget ligand ethynyl-2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiophene(L5). The synthetic route is shown in FIG. 12. Excitation of the ligandwith λ≦352 nm light resulted in the formation of the close form,corresponding to the photocyclization product.

Upon reaction with dichlorobis(triethylphosphine)platinum(II), the openform of the corresponding complex (8) undergoes photocyclization withthe excitation up to λ≦430 nm. The electronic absorption data of ligand(L5) and complex (8) are summarized in Table 8. The representativeelectronic absorption spectral changes of complex (8) in dichloromethanesolution upon photo-irradiation are shown in FIG. 13.

TABLE 8 Absorption maximum Compound Configuration (in dichloromethane)λ_(abs)/nm (L5) Open form 260, 294, 304, 314sh (L5) Close form 300, 382,554 (8) Open form 260sh, 296, 304, 318sh, 384 (8) Close form 372, 560

1. The photochromic compound which is a diarylethene-containingcoordination compound in which the diarylethene contains part of amonocyclic or polycyclic structure with one or more donor atoms orheteroatoms coordinated to a coordination unit [M], which contains anacceptor atom, M, expressed by the general formula (I):

where unit B is porphyrin or azaporphyrin, each donor atom X isnitrogen, n is 3, [M] represents a coordination unit containing anacceptor atom M wherein the acceptor atom M is rhenium(I), zinc(II),ruthenium(II), osmium(II), rhodium(III), iridium(III), gold(III),gold(I), silver(I), copper(I), copper(II), platinum(II), palladium(II),iron(II), cobalt(III), chromium(III), cadmium(II), or boron(III), R₁ andR₆ individually represent an alkyl group or an alkoxy group, and R₂ toR₅ individually represent atoms or groups selected from hydrogen atom,halogen atom, hydroxyl group, alkyl group, alkoxy group, alkynyl group,cyano group, nitro group, alkylcarbonyl group, alkoxycarbonyl group,perfluoroalkyl group, aryl group, cycloalkyl group, arylcarbonyl group,aryloxycarbonyl group, mono- or dialkylaminocarbonyl group,alkylcarbonyloxy group, arylcarbonyloxy group, aryloxy group,alkoxycarbonyl group, and aryloxycarbonyloxy group.
 2. The photochromiccompound in accordance with claim 1, wherein unit B is a porphyrin. 3.The photochromic compound in accordance with claim 2, wherein R₁ and R₆represent methyl groups, and R₃ and R₄ represent hydrogen atoms.
 4. Thephotochromic compound in accordance with claim 2, wherein R₂ and R₅represent hydrogen atoms.
 5. The photochromic compound in accordancewith claim 2, wherein R₂ and R₅ represent methyl groups.
 6. Thephotochromic compound in accordance with claim 2, wherein R₂ end R₅represent bromine atoms.
 7. The photochromic compound in accordance withclaim 2, wherein M represents zinc(II).
 8. The photochromic compound inaccordance with claim 2, wherein M represents platinum (II).